The present invention relates generally to industrial turbine engines, and more specifically, to thermocouple failure detection therein.
Industrial power generation gas turbine engines include a compressor for compressing air that is mixed with fuel and ignited in a combustor for generating combustion gases. The combustion gases flow to a turbine that extracts energy for driving a shaft to power the compressor and produces output power for powering an electrical generator, for example. The turbine is typically operated for extended periods of time at a relatively high base load for powering the generator to produce electrical power to a utility grid, for example. Exhaust emissions from the combustion gases are therefore a concern and are subjected to mandated limits.
Gas turbine combustors are being developed which employ lean premixed combustion to reduce emissions of gases such as NOx (nitrogen oxides). One such combustor comprises a plurality of burners attached to a single combustion chamber. Each burner includes a flow tube with a centrally disposed fuel nozzle comprising a center hub which supports fuel injectors and swirl vanes. During operation, fuel is injected through the fuel injectors and mixes with the swirling air in the flow tube, and a flame is produced at the exit of the burner. The combustion flame is stabilized by a combination of bluffbody recirculation behind the center hub and swirl-induced recirculation. Because of the lean stoichiometry, lean premixed combustion achieves lower flame temperature and thus produces lower NOx emissions.
These premixed systems, however, are susceptible to an unpredictable phenomena commonly referred to as xe2x80x9cflashback.xe2x80x9d Flashbacks can be caused by any of a number of events, including ignition of impurities in fuel or ignition during mode switching when the flames are in a transient phase. When flashback occurs, a flame enters zones or cavities of the combustor chamber which may not be designed to contain flames. A flame can also move unexpectedly into combustor cavities specified for firing modes other than the combustion mode being exercised at the time of the flashback occurrence. Both types of flashback occurrences result in a loss of combustion control and can additionally cause heating and melting of combustor parts, such as fuel nozzles, for example, that are not designed to withstand excessive heating. An operator generally has no method of recognizing the occurrence of a flashback until the combustor sustains damage.
An event monitor may be implemented that attempts to detect flashback events and severe crack events by monitoring exhaust thermocouple readings and the associated NOx values. This method has been shown to be effective. A deviation of a thermocouple reading from the expected, however, can also be due to a thermocouple failure. Accordingly, for an event monitor to be accurate, it is necessary to distinguish between a thermocouple failure and a flashback event or liner crack event.
Therefore, it is apparent from the above that there exists a need in the art for a method of detecting failed exhaust thermocouples in a power turbine.
A method of thermocouple failure detection in power generation turbines first comprises creating redundancy estimates from temperature readings generated by thermocouples. Next, an expected value is predicted from each temperature reading. The temperature readings and the redundancy estimates are compared with the expected value. Next, the redundancy estimates and the expected values are fused to generate a fused thermocouple value. Finally, a thermocouple confidence is generated by comparing the fused thermocouple value and the temperature readings.